Wind as a source of energy is a concept that has been promoted from ancient time. According to historical sources, there is evidence which shows that windmills were in use in Babylon and in China as early as 2000 B.C.
Wind is used as a source of energy for driving horizontal axis and vertical axis windmills. Horizontal axis windmills have been used extensively to drive electrical generators, however they suffer from several disadvantages, including the need for a laminar (non-turbulent) horizontal air inflow, danger to birds and air traffic, obscuring the landscape with banks of rotating windmills, and in the case of large diameter horizontal axis propellers, supersonic speeds at the tips of the rotors.
Vertical axis wind turbines (VAWT) seams to suffer less from the disadvantages of the horizontal axis wind turbines; however so far the VAWT are not often used in commercial applications.
Usually the current wind turbine technologies extract the wind energy via their blades using lift or drag to turn their rotor. Very few of prior art wind turbine technologies are using the vortex to extract the wind power energy. Those that use the vortex are doing it mainly as a way to rapidly exhaust the airflow from the wind turbine rather than as a significant increase in wind power extraction.
An example of vertical axis wind turbine (VAWT) using the vortex to exhaust the airflow is shown in British Patent No. 185,939 to Hashimoto et al. that discloses a vertical axis wind turbine where the airflow creates a natural vortex in the center of the rotor and it is exhausted via an exhaust chamber system situated on top of the turbine. The novelty of the Hashimoto invention is a cowl-like casing that creates opposite flows to force the air to be exhausted as soon as possible towards the centre of the turbine and via the exhaust chamber. In the Hashimoto design the functioning objective is to have the airflow exhausted as soon as possible after it passed the rotor blades. Any airflow that escapes to the other chambers of the rotor, instead of being directly exhausted, will contribute negatively to the overall efficiency of the turbine. One of the major drawbacks of that design is the fact that the turbine has a very complex exhaust chamber connected rigidly to the cowl-like casing that has to rotate according to the wind direction. Moreover the Hashimoto design does not have any means to extract more energy from the naturally created vortex, using that vortex only as a way to rapidly exhaust the airflow.
U.S. Pat. No. 1,545,633 to A. Bender discloses another vertical axis wind turbine having two sets of blades one on top of the other, as such that the upper series of blades act as a deflector to exhaust the airflow towards a central exhaust cylinder (stack) having inside that stack a third propeller intended to extract more energy from the exhausted airflow. The Bender's VAWT has a central cylindrical hollow core closed in the bottom by a circular flange. One of the major drawbacks of that design is the fact that the vortex created in the upper dome can escape only via the upper exhaust stack having inside the third propeller. That third propeller is covering the whole sectional surface of the exhaust cylinder creating a pressure to the exhaust of the airflow. The pressure created by the third propeller is naturally regulated, due to the free flow dynamics of the wind, by having at the exterior less wind going towards the turbine and having more wind going around the turbine, which translates in lower efficiency of the disclosed design.
U.S. Pat. No. 4,452,562 to Cheng-Ting Hsu discloses a tornado type wind turbine that uses the vortex generated in a collecting tower. The collecting tower as well as the lower intake chamber needs to face the wind, so it requires a yaw mechanism to orient it into the wind.
Further, U.S. Pat. No. 4,070,131 to James Yen discloses an outer tornado type turbine that has a stationary structure in which a vortex is created. The stationary structure has vertical stationary vanes that allow the airflow to enter in the center of the structure in a generally circular path to allow the creation of the vortex. One of the major drawbacks of that design is that, being in a free flow dynamics system such as the natural wind conditions, it requires a considerable size of such a turbine to be able to create a vortex that will drive an electrical generator.
International Patent Application No. PCT/CA01/01310 (Louis Michaud) discloses an induced vortex turbine where the vortex is created by artificially heating the air within the circular tower and mixing it with warmer airflows.
Further, U.S. Pat. No. 1,600,105 to Fonkiewicz discloses another induced vortex turbine where the vortex is created by artificially heating the air at the base of a relatively large circular tower made of concrete, cement blocks or bricks.
U.S. Pat. No. 1,783,669 (Oliver) discloses a horizontal axis system turbine in an air augmenter tubular body where a plurality of propellers is installed to extract the wind energy. It is assumed that the airflow will create a vortex inside the tubular body due to the rotation of the propellers. The design has many shortcomings due to impracticality of turning the whole structure to face the wind. Moreover the design do not allow for a proper creation of a vortex. Inside the tubular body the close installation of the propellers creates a highly turbulent airflow rather than a proper vortex.
U.S. Patent Application No. 2004/0183310 (Mowll) discloses another concept of horizontal axis wind turbine comprising an airflow augmenter defined in the patent application as vortex housing. One of the major drawbacks of that design is the fact that the vortex housing needs to face the wind, so it requires a yaw mechanism to orient it into the wind. Moreover, the vortex housing is only an augmenter to take the airflow on a larger surface to direct it towards a smaller surface where the propeller is installed. In that design the vortex is created only behind the propeller, in the small exhaust channel where there are no other wind energy extraction means.
U.S. Pat. No. 4,414,477 to Mewburn-Crook discloses a drag type of vertical axis wind turbine with stator vanes and having helical stator fins on the tower bellow the turbine to create an upward pushing airflow to facilitate the exhaust of the wind from the wind turbine. The intent of the design with the helical stator fins on the tower is to create an upwardly vortex that will assist the rotation of the upper turbine. The shortcoming of this design is that no proper vortex is created in that configuration as the turbine fans extends radially to the central shaft not creating any type of central whole where the vortex might have been created. The upwardly helical airflow, intended to be guided by the stator fins, encounters the rotational turbine blades as well as the turbulences created by the rotation of the upper turbine fan and any desired vortex is annihilated.
International Patent Application No. PCT/CA2006/000803 to Arrowind discloses a Savonious type of vertical axis wind turbine where the blades define an open area in the center of the rotor section to create a vertical vortex air. Regarding the intended vortex, the shortcoming of that design is the fact that there are no means to control and maintain the vortex or extract any significant energy from it.
International Patent Application No. PCT/CA2007/001200 attributed to the applicant discloses a boundary layer wind turbine having openings near the center of the disks to create a vortex intended to contribute to increase the rotation of the turbine and as a consequence its efficiency. Regarding the created vortex, the shortcoming of that design is the fact that there are no means to control the vortex or significantly extract its energy.
A disadvantage of all the horizontal and vertical axis windmills of the prior art mentioning vortex phenomenon relates to their inability to control and maintain the vortex or extract its energy beyond the kinetic energy of the rotating airflow. Unfortunately, in most cases the prior art do not takes into consideration all the complex aspects of the vortex phenomenon.
There is therefore a need for a wind turbine that uses the vortex properties and is able to extract its energy beyond the kinetic energy of the rotating airflow, taking into consideration all the complex aspects of the vortex phenomenon in free fluid dynamics conditions.